Ethanol may be produced from grain-based feedstocks (e.g., corn, sorghum/milo, barley, wheat, soybeans, etc.), from sugar (e.g., sugar cane, sugar beets, etc.), or from biomass (e.g., lignocellulosic feedstocks, such as switchgrass, corn cobs and stover, wood, or other plant material). The most common raw material for ethanol production, however, is the starch contained within corn.
In a conventional ethanol plant, corn kernels are cleaned and milled to prepare starch-containing material for processing. Corn kernels may also be fractionated to separate the starch-containing material (e.g., endosperm) from other matter (such as fiber and germ). The starch-containing material is slurried with water and liquefied to facilitate saccharification, where the starch is converted into sugar (e.g., glucose), and fermentation, where the sugar is converted by an ethanologen (e.g., yeast) into ethanol. The fermentation product is beer, which comprises a liquid component, including ethanol, water, and soluble components, and a solids component, including unfermented particulate matter (among other things). The fermentation product is sent to a distillation system where the fermentation product is distilled and dehydrated into ethanol. The residual matter (e.g., whole stillage) comprises water, soluble components, oil, and unfermented solids (e.g., the solids component of the beer with substantially all ethanol removed, which may be dried into dried distillers grains (DDG) and sold, for example, as an animal feed product). Other co-products (e.g., syrup and oil contained in the syrup), may also be recovered from the whole stillage. Water removed from the fermentation product in distillation may be treated for re-use at the plant.
Many traditional corn to ethanol production facilities employ high heat to cook (gelatinize) the starch-containing material to facilitate liquefaction prior to saccharification. One result from the cooking of the starch slurry is that endogenous enzymes, which are native to the corn, are rendered inoperative. Thus, in cooked systems, corn quality has traditionally been purely defined by the total fermentable starch content of the corn. However, as non-cooking processes (raw starch hydrolysis) become more prevalent, it has become clear that good quality corn is no longer merely synonymous with starch content. In these ethanol production plants, the slurry is subjected to simultaneous saccharification and fermentation. There is abundant evidence of presence of esterases in grains (Ward and Bamforth, 2002). The endogenous esterase activity in grains can serve as an indicator for the activities of specific enzymes present in the feedstock (such as amylases and endoproteases). (Jones, 2005). Since the activity of endogenous enzymes within feedstock grains has been linked to the temperature that the grains are subjected to, when non-cooked ethanol production is utilized, the endogenous enzyme activity may significantly impact saccharification efficiency. (Kumar et al., 2005). Thus, corn or other feedstock which retain high levels of endogenous enzymes are found to produce higher fermentation efficiencies. (Setiawan et al., 2010). Again, this is due in part to the fact that the naturally present enzymes are preserved and therefore aid in the saccharification process.
In addition to ethanol production, assessment of feedstock quality, as indicated by endogenous enzyme activity, may have a large impact upon other applications of the feedstock. Prominently, feedstock quality may be directly correlated to germination efficiency of seed quality feedstock. Further, for wet millers, it may be advantageous to have feedstock with higher endogenous enzyme activity, as more active feedstock may process better in a wet mill.
Currently there is no rapid and effective method available to determine quality of corn based on the levels of endogenous enzymes present. Instead, routine quality tests such as moisture content, presence of foreign material, broken grain, and test weight are performed on the incoming corn. (Evers et al., 2002). However, those tests do not indicate if the corn has more enzyme activity (such as amylases which convert starch into sugars), and thus have higher saccharification efficiency. (Ziegler, 1999). Recently, there has been renewed interest in developing Near Infrared Spectroscopy (NIR) methods for assessing the fermentable starch in superior corn hybrids by companies such as DuPont Pioneer; however, such systems are still under development, and show poor correlation between NIR readings and corn fermentation yields.